4.4.3. Film WVP

The WVP was determined using the Zhang et al. [56] technique with the necessary changes. In total, 10 g of anhydrous CaCl<sup>2</sup> was placed in a glass cup with a diameter of 4 cm, and a film measuring 10 × 10 cm was placed on top, supported by rubber strands. The cups were then piled inside the desiccator and filled with sodium chloride saturation solution (75 RH). For up to seven hours, the cup's weight was registered every hour. Using linear regression, the slope of each line (K) (g/h) was determined. Equation (1) was used to calculate the WVP values.

$$\text{WVP} = \frac{(\text{Film thickness}) \times \text{K}}{(\text{Vapor pressure difference}) \times (\text{Film area})} \tag{1}$$
